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Volcanic pyroclastic deposits generally have a metastable and collapsible structure, which may lead to their liquefaction under monotonic, cyclic, and dynamic loading. Their structure could be partly attributed to the nature of the pyroclastic particles, especially their lightweight, fragile and porous features. In comparing the results of monotonic and cyclic undrained triaxial tests performed on Cervinara soil, the steady-state concept is used to define the occurrence of liquefaction. A significant part of the experimental program on Rangiriri soil is carried out to highlight the role of the fragility of pyroclastic particles on the occurrence of liquefaction. The comparison between the results obtained on the two types of pyroclastic soils shows the possibility of explaining the undrained mechanism of pore pressure buildup using the state parameter ψ. The parameter ψ seems to be useful also in comparing the results obtained on pyroclastic soils with those on ordinary sands. The state parameter has a clear physical significance that could be used to define a more reliable model of undrained pore pressure buildup for soils of different natures. [ABSTRACT FROM AUTHOR]

In the last ten thousand years, the explosive activity of some volcanic centers has blanketed with pyroclastic soils the major part of Campania Region, Southern Italy. Experience shows that the sloping deposits may be mobilized by long-lasting precipitations, leading to rapid and sometimes catastrophic flow-type slope movements. This paper summarizes the present knowledge on this subject based on the results of both laboratory tests and experiments and on a review of the main data provided by field surveys. In particular, a careful examination and analysis of the available elements highlight the key role played by lithological and morphological details on failure and post-failure mechanisms, thus affecting landslide hazard. In fact, it is shown that deposition mode and grain size, slope angle, and morphology strongly affect the type of post-failure movement, which may take the features of a debris avalanche, of a debris flow, or of a flowslide and may lead (or not) to soil liquefaction, a mechanism that strongly affects both displacement rate and run-out. [ABSTRACT FROM AUTHOR]

Abstract: Campania Region (Italy), one of the most densely populated areas in Europe, is probably the one with the highest risk of landslide. A large part of the region is covered by unsaturated cohesionless pyroclastic deposits subjected to rainfall-induced landslides. According to experience, these can display different features and magnitude. The most catastrophic landslides are liquefied debris flows which periodically occur on steep slopes, causing death and destruction in areas located downslope. Therefore, zoning of those areas which can be the source of liquefied debris flow is necessary. The paper reports some useful elements for zoning based on infinite slope analysis, accounting for the results of recent research on the mechanics of rainfall-induced landslides in pyroclastic soils. [Copyright &y& Elsevier]

This article analyzes shallow flowslides triggered by intense rainfalls on natural slopes, covered by loose unsaturated pyroclastic soils. Pyroclastic soils have been deposited some thousands of years ago during the eruptions of Vesuvius and other volcanoes rising in the same area. Pyroclastic covers along the upper part of the slopes are rather thin and consist of alternating layers of unsaturated volcanic ash and pumice with palaeosoil interbeds. Soil layers are parallel to the ground surface. Static liquefaction is the fundamental mechanism that is responsible for flowslide initiation, mostly in loose granular soils constituting dumps, stockpiles and tailing dams or covering natural slopes.